1. Field of the Invention
The present invention relates to a device for measuring a flow rate of air, for example, measuring a flow rate of intake air to an engine.
2. Description of the Related Art
In the related art, a device has been proposed wherein a flow rate measurement pipe is provided in an air intake pipe of an engine of a vehicle, and an electric heater consisting of a platinum resistor wire and a temperature compensation resistor for detecting a temperature of air are provided in the flow rate measurement pipe, so that a flow rate of intake air is measured with reference to signals output from the flow rate measurement pipe.
Although the structure of this conventional flow rate measuring device is compact and simple, a current must be supplied to the electric heater to maintain it at a constant temperature, and the current value is output as an analog signal corresponding to the flow rate. Therefore, when this output signal is to be converted into a digital signal by a microcomputer and the like, a high precision A/D converter must be used, resulting in a high production cost.
Also, a ripple component due to an irregular air flow rate is superimposed on the output signal. Therefore, when the output signal is directly converted into a digital signal, precision is undesirably degraded due to that ripple component.